linux-kernel - Re: [PATCH] usb: typec: pd: Add symlink to linked device

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Date:   Mon, 21 Nov 2022 07:35:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Benson Leung <bleung@...omium.org>
Subject: Re: [PATCH] usb: typec: pd: Add symlink to linked device

On Mon, Nov 21, 2022 at 06:20:39AM +0000, Prashant Malani wrote:
> There exists a symlink from a device to its USB Power Delivery object,
> but not the other way around. Add a symlink from the USB PD object to
> the device which it's associated with, and call it "device".
> 
> This is helpful to identify said device (a Type-C peripheral for
> example) during uevents, since during USB PD object
> creation/destruction, a uevent is generated for the PD object,
> but not the device linked to it.
> 
> Cc: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Cc: Benson Leung <bleung@...omium.org>
> Signed-off-by: Prashant Malani <pmalani@...omium.org>
> ---
>  .../ABI/testing/sysfs-class-usb_power_delivery       |  6 ++++++
>  drivers/usb/typec/pd.c                               | 12 ++++++++++--
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-usb_power_delivery b/Documentation/ABI/testing/sysfs-class-usb_power_delivery
> index ce2b1b563cb3..e7d19193875f 100644
> --- a/Documentation/ABI/testing/sysfs-class-usb_power_delivery
> +++ b/Documentation/ABI/testing/sysfs-class-usb_power_delivery
> @@ -4,6 +4,12 @@ Contact:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
>  Description:
>  		Directory for USB Power Delivery devices.
>  
> +What:		/sys/class/usb_power_delivery/.../device
> +Date:		November 2022
> +Contact:	Prashant Malani <pmalani@...omium.org>
> +Description:
> +		Symbolic link to the directory of the device to which the USB PD object is linked.

Line is way too long.

But wait, a "device" has a specific meaning in a sysfs file, and that is
not what is happening here.

Please don't make fake "device" symlinks when these are not really using
a device here.  Either fix it up to properly use the device structures
in the code, or call this something else.

What in userspace wants to see this symlink?

thanks,

greg k-h